The invention relates to a method for producing heteroepitaxial diamond layers from the vapor phase on a silicon substrate, as well as to layers produced by this method and the use thereof.
As is known from M. W. Geis et al, IEEE Electron Device Letters EDL-8, 1987, 341 and M. W. Geis et al, J. Vac. Sci. Technol., A 6, 1988, 1953, as a result of its excellent physical properties such as
band gap 5.5 eV hole mobility 1800 cm.sup.2 /V.sub.s electron mobility 2000 cm.sup.2 /V.sub.s electron saturation drift rate 2 .times. 10.sup.7 cm/s disruptive field 1 .times. 10.sup.7 V/cm thermal conductivity 20 W/cmK relative permativity 5.7
diamond is an excellent material, which is suitable for high temperature, high frequency and high power semiconductor components.
After Japanese scientists described at the beginning of the 1980's that diamond can be synthesized as a layer or coating from gaseous substances, numerous efforts were made throughout the world to find new applications for this promising material with its great technological potential.
The efforts to use CVD-diamond as an active or passive electronic material have failed up to now because it has not been possible to heteroepitaxially deposit diamond from the most standard substrate, namely silicon. However, epitaxy is the prerequisite for obtaining electrical characteristics as are expected of such layers. In order to develop and test new solutions for this problem, numerous developments have been made in the past. Only localized epitactic growth has been obtained on silicon substrates (D. G. Jeng, H. S. Tuan, R. F. Salat and G. J. Fricano, Appl. Phys. Lett. 56, 1968 (1990); J. Narayan, A. R. Srivatra, M. Peters, S. Yokota and K. V. Ravi, Appl. Phys. Lett. 53, 1823, (1988)). Although heteroepitaxy is successful on C-BN, this is only so on particles, because at present it is not possible to produce a crystalline, large-surface C-BN (S. Koizumi, T. Murakami and T. Inuzuka and K. Suzuki, Appl. Phys. Lett. 57, 563 (1990)). On silicon carbide (1-wafer), a carrier material which is very difficult to produce, only a partially oriented growth of diamond (50% of the grown crystals) has been performed with bias nucleation (B. R. Stoner and J. T. Glass, Appl. Phys. Lett. 60, 698 (1992)).
Of late further publications have appeared which deal with this problem.
In physical review B V. 45, no.19, p.11067ff, Stoner et al reported on the deposition of diamond on Si. The procedure was such that a two-stage process is proposed, involving a pretreatment (nucleation) accompanied by the application of a negative bias voltage in the case of a 2% methane/hydrogen plasma. This was followed by a growth phase while maintaining the bias voltage. The crystallites in the layers obtained have a random orientation.
The working group of Yugo et al (Appl. Phys. Lett. 58 (10), p.1036ff) have also proposed a two-stage process. The first stage is performed accompanied by the application of a negative bias voltage with a CH.sub.4 /H.sub.2 plasma, the methane proportion being 40%. The diamond deposition is carried out without bias under "normal" conditions (approx. 0.5% methane in H.sub.2). However, this process leads to randomly oriented, polycrystalline layers and not to heteroepitaxial layers.
Thus, no method is known which makes it possible to heteroepitaxially deposit diamond on the most widespread substrate, namely Si.